1. Field of the Invention
The present invention generally relates to a semiconductor device and a method of manufacturing the same. The present invention particularly relates to a method of manufacturing a semiconductor device provided with electrodes formed on a semiconductor substrate, barrier metals formed on respective electrodes and protruded electrodes joined to the electrodes via the barrier metals.
Recently, there is a decrease in the sizes of semiconductor devices. It is known to use protruded electrodes such as bumps as external connection terminals of the miniaturized semiconductor devices. The semiconductor devices having protruded electrodes may be a BGA (Ball Grid Array) type semiconductor device or a CSP (Chip Size Package) type semiconductor device.
Also, the semiconductor devices require higher reliability, and thus, it is necessary that protruded electrodes also realize higher reliability.
2. Description of the Related Art
FIG. 1 is a side view of an example of a semiconductor device of a related art having bumps and electrode pads. Here, FIG. 1 shows a semiconductor device 1 of a general CSP type. As shown in FIG. 1, the semiconductor device 1 has a plurality of electrode pads 3 provided on a circuit forming surface 2a of the semiconductor chip 2. Each electrode pad 3 is provided with a bump 4 which serves as an external connection terminal.
FIG. 2 is an enlarged view showing a region around the electrode pad 3 provided on the semiconductor device 1 of FIG. 1. The electrode pad 3 includes an electrode 5 and a barrier metal 10. As shown in FIG. 2, the bump 4 is not directly formed on the electrode 5, but is joined to the electrode 5 via the barrier metal 10 provided on the electrode 5. The detailed structure of the semiconductor device 1 will be described below.
The circuit forming surface 2a of the semiconductor chip 2 is provided with an insulating layer 6 for protecting the circuit forming surface 2a. The insulating layer 6 is provided with openings 7 at positions corresponding to the electrodes 5 such that the electrodes 5 are exposed via the openings 7.
The barrier metal 10 has a layered structure of a first conductive metal layer 11, a second conductive metal layer 12, and a third conductive metal layer 13. The barrier metal 10 prevents the bump 4 from diffusing into the electrode 5. For example, when the bump 4 is made of solder and a gold (Au) plating is applied on the electrode 5, and if the bump 4 is directly joined to the electrode 5, the solder will diffuse into the gold plating of the electrode 5. This causes a decrease in strength of the diffused part, which may result in the peeling off of the bump 4 from the electrode 5. The barrier metal 10 prevents the bump 4 from diffusing into the electrode 5 and thus prevents the bump 4 from being peeled off from the electrode 5.
The first conductive metal layer 11 is provided at a position nearest to the semiconductor chip 2 or at the lowermost position. This first conductive metal layer 11 is made of a material having a good joining property with the electrode 5. The second conductive metal layer 12 is provided on the first conductive metal layer 11. This second conductive metal layer 12 is made of a material having a good joining property with the first conductive metal layer 11. The third conductive metal layer 13 is provided on the second conductive metal layer 12. This third conductive metal layer 13 is made of a material having a good joining property with the second conductive metal layer 12 and the bump 4. Also, the third conductive metal layer 13 should be made of a material which can prevent the diffusion of the bump 4.
The semiconductor device 1 is manufactured in the following manner. First, the barrier metals 10 are formed. In order to manufacture the barrier metal 10, the first conductive metal layer 11 is formed on the semiconductor chip 2 such that the first conductive metal layer 11 is electrically connected to the electrode 5. Then, the second conductive metal layer 12 is laminated on the first conductive metal layer 11. Subsequently, a resist having openings corresponding to predetermined shapes of the barrier metals is formed on the second conductive metal layer 12. With this resist being provided on the second conductive metal layer, the third conductive metal layer 13 is formed. Thereafter, the resist is removed. Further, unwanted parts of the first and second conductive metal layers 11 and 12 are removed by etching. Thus, the barrier metal 10 is obtained.
The bumps 4 serving as external connection terminals are formed by transferring solder balls onto the barrier metals 10 and heating the solder balls so that the solder balls will be joined to the barrier metals 10.
After the bumps 4 have been formed as described above, a testing step is carried out. As shown in FIG. 3, probes 14 connected to a tester or a testing device (not shown) are brought in contact with the bumps 4. This may be referred to as “probing”. Then, test signals from the tester are supplied to the semiconductor chip 2 via the probes 4. Thus, a predetermined test such as a reliability test or an operational test can be implemented on the semiconductor chip 2. Thereby, good semiconductor devices are selected.
With the method of manufacturing the semiconductor device of the related art, the testing step is carried out after the bumps 4 have been formed on the barrier metals 10. Therefore, the probes 14 should be connected to the bump 4. However, it is difficult to properly connect the probe 14 to the bump 4 having a spherical shape. Also, according to the recent miniaturization of the semiconductor device 1, further fine-pitched structures, such as an area array, have been introduced. Then, there arises a problem that it is even more difficult to properly connect the probe 14 to the bump 4 having a spherical shape.
Also, when the probe 14 is directly probed on the bump 4, the material of the bump 4 will adhere to the tip part of the probe 14. Examples of the material forming the bump 4 may be tin (Sn) or lead (Pb). On the other hand, generally, the tip part of the probe 14 is provided with a plated part 15. For example, when the probe 14 is made of palladium (Pd), the plated part 15 may be of gold.
It is well known that tin reacts with gold. Therefore, if the material of the bump 4 adheres onto the tip part of the probe 14, the probe 14 will be degraded over a several usage. This results in a drawback that the reliability of the testing step is reduced. Also, there is a drawback that the testing cost increases since a frequent replacement of the costly probes 14 is necessary.